(a) Field of the Invention
The present invention relates to a switching operation frequency modulation device for reducing an output voltage ripple, and a switch mode power supply (SMPS).
(b) Description of the Related Art
An SMPS rectifies an input AC voltage into an input DC voltage, and converts the input DC voltage into a DC output voltage of another level. Such SMPS is mainly used for battery power supply devices such as power electronic devices, particularly, mobile phones and laptop computers.
An output voltage of the SMPS is increased/decreased by an increase/decrease of an input DC voltage (hereinafter, input voltage). That is, a ripple of the input voltage influences the output voltage of the SMPS, and an output voltage ripple in which the output voltage is increased/decreased by the input voltage is generated.
Switching noise that is generated by a switching operation when the SMPS is operated can cause electromagnetic interference (EMI) generation in equipment including the SMPS. Switching noise represents a noise component that occurs by a switching operation frequency of a switch configuring the SMPS and a harmonics component. When the EMI occurs, operations of peripheral electronic devices of the device including the SMPS are jammed. A method for suppressing occurrence of EMI is a method for modulating the switching operation frequency. However, the frequency modulation method generates an output voltage ripple according to switching operation frequency modulation, which is added to an output voltage ripple component by the input voltage's ripple to generate a greater output voltage ripple.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.